In the use of an "artificial kidney", dialysis of the patient's blood requires some means of withdrawing the blood from the patient's body and returning the same after treatment. With cannulae, providing permanent tubular connection to the patient, connection of the patient to the dialyzer apparatus is facilitated. However, a patient may not tolerate this arrangement because of infection or the like. Alternatively, plural hypodermic needles may be inserted in a patient's vein after insertion of a fistula between a vein and an artery, with one needle being utilized for withdrawal of blood while a second needle is employed to return blood to the vein. A more desirable system would avoid the requirement for repeated insertion of both needles.
A prior art single needle system withdraws and returns blood via the same hypodermic needle and includes a pair of clamp valves employed in two connections to the hypodermic needle so that blood can be alternately withdrawn and returned therethrough. In this system the valves are solenoid operated in response to pressure detected at a dialyzer output. However, pumping in such a system tends to produce a vacuum at the pump inlet, flattening the plastic tubing and causing cessation of system operation. Moreover, the addition of solenoid operated valves represents additional equipment and expense.